The present invention relates to a system for controlling the production of hydrocarbons and other fluids from downhole wells. More particularly, the invention relates to a system for providing hydraulic control signals and power through the same hydraulic line, and for providing integrated control of multiple well tools with a minimal number of hydraulic lines.
Various tools and tool systems have been developed to control, select or regulate the production of hydrocarbon fluids and other fluids produced downhole from subterranean wells. Downhole well tools such as sliding sleeves, sliding side doors, interval control lines, safety valves, lubricator valves, and gas lift valves are representative examples of control tools positioned downhole in wells.
Sliding sleeves and similar devices can be placed in isolated sections of the wellbore to control fluid flow from such wellbore section. Multiple sliding sleeves and interval control valves (ICVs) can be placed in different isolated sections within production tubing to jointly control fluid flow within the particular production tubing section, and to commingle the various fluids within the common production tubing interior. This production method is known as "comingling" or "coproduction". Reverse circulation of fluids through the production of tubing, known as "injection splitting", is performed by pumping a production chemical or other fluid downwardly into the production tubing and through different production tubing sections.
Wellbore tool actuators generally comprise short term or long term devices. Short term devices include one shot tools and tool having limited operating cycles. Long term devices can use hydraulically operated mechanical mechanisms performing over multiple cycles. Actuation signals are provided through mechanical, direct pressure, pressure pulsing, electrical, electromagnetic, acoustic, and other mechanisms. The control mechanism may involve simple mechanics, fluid logic controls, timers, or electronics. Motive power to actuated the tools can be provided through springs, differential pressure, hydrostatic pressure, or locally generated power.
Long term devices provide virtually unlimited operating cycles and are designed for operation through the well producing life. One long term safety valve device provides fail safe operating capabilities which closes the tubing interior with spring powered force when the hydraulic line pressure is lost. Combination electrical and hydraulic powered systems have been developed for downhole use, and other systems include sensors which verify proper operation of tool components.
Interval control valve (ICV) activation is typically accomplished with mechanical techniques such as a shifting tool deployed from the well surface on a workstring or coiled tubing. This technique is expensive and inefficient because the surface controlled rigs may be unavailable, advance logistical planning is required, and hydrocarbon production is lost during operation of the shifting tool. Alternatively, electrical and hydraulic umbilical lines have been used to remotely control one or more ICVs without reentry to the wellbore.
Control for one downhole tool can be hydraulically accomplished by connecting a single hydraulic line to a tool such as an ICV or a lubricator valve, and by discharging hydraulic fluid from the line end into the wellbore. This technique has several limitations as the hydraulic fluid exits the wellbore because of differential pressures between the hydraulic line and the wellbore. Additionally, the setting depths are limited by the maximum pressure that a pressure relief valve can hold between the differential pressure between the control line pressure and the production tubing when the system is at rest. These limitations restrict single line hydraulics to low differential pressure applications such a lubricator valves and ESP sliding sleeves. Further, discharge of hydraulic fluid into the wellbore comprises an environmental discharge and risks backflow and particulate contamination into the hydraulic system. To avoid such contamination and corrosion problems, closed loop hydraulic systems are preferred over hydraulic fluid discharge valves downstream of the well tool actuator.
Certain techniques have proposed multiple tool operation through a single hydraulic line. U.S. Pat. No. 4,660,647 to Richart (1987) disclosed a system for changing downhole flow paths by providing different plug assemblies suitable for insertion within a side pocket mandrel downhole in the wellbore. In U.S. Pat. No. 4,796,699 to Upchurch (1989), an electronic downhole controller received pulsed signals for further operation of multiple well tools. In U.S. Pat. No. 4,942,926 to Lessi (1990), hydraulic fluid pressure from a single line was directed by solenoid valves to control different operations. A return means in the form of a spring facilitated return of the components to the original position. A second hydraulic line was added to provide for dual operation of the same tool function by controlling hydraulic fluid flow in different directions. Similarly, U.S. Pat. No. 4,945,995 to Thulance et al. (1990) disclosed an electrically operated solenoid valve for selectively controlling operation of a hydraulic line for opening downhole wellbore valves.
Other downhole well tools use two hydraulic lines to control a single tool. In U.S. Pat. No. 3,906,726 to Jameson (1975), a manual control disable valve and a manual choke control valve controlled the flow of hydraulic fluid on either side of a piston head. In U.S. Pat. No. 4,197,879 to Young (1980), and in U.S. Pat. No. 4,368, 871 to Young (1983), two hydraulic hoses controlled from a vessel were selectively pressurized to open and close a lubricator valve during well test operations. A separate control fluid was directed by each hydraulic hose so that one fluid pressure opened the valve and a different fluid pressure closed the valve. In U.S. Pat. No. 4,476,933 to Brooks (1984), a piston shoulder functioned as a double acting piston in a lubricator valve, and two separate control lines were connected to conduits and to conventional fittings to provide high or low pressures in chambers on opposite sides of the piston shoulder. In U.S. Pat. No. 4,522,370 to Noack et al. (1985), a combined lubricator and retainer valve was operable with first and second pressure fluids and pressure responsive members, and two control lines provided two hydraulic fluid pressures to the control valve. This technique is inefficient because two hydraulic lines are required for each downhole tool, which magnifies the problems associated with hydraulic lines run through packers and wellheads.
Instead of multiple hydraulic lines, other techniques have attempted to establish an operating sequence. In U.S. Pat. No. 5,065,825 to Bardin et al. (1991), a solenoid valve was operated in response to a predetermined sequence to move fluid from one position to another. A check valve permitted discharge of oil into a reservoir to replenish the reservoir oil pressure. Other systems use electronic controllers downhole in the wellbore to distribute, however the electronics are susceptible to temperature induced deterioration and other reliability problems.
Multiple hydraulic lines downhole in a wellbore can extend for thousands of feet into the wellbore. In large wellbores having different production zones and multiple tool requirements, large numbers of hydraulic lines are required. Each line significantly increases installation cost and the number of components potentially subject to failure. Accordingly, a need exists for an improved well control system capable of avoiding the limitations of prior art devices. The system should be reliable, should be adaptable to different tool configurations and combinations, and should be inexpensive to deploy.